There has long been a desire to formulate a curing agent which is simultaneously storage stable, is immediately compatible with conventional epoxy resins, and is sufficiently reactive with epoxy resins that the system will cure in a wide range of temperatures, even as low as 4.4.degree. C., within a 24 hour period in the absence of external accelerators if possible. Typical amine curing agents have primary amine groups, and stored or used in low temperature curing conditions or in high humidity environments, produce in the final cured product the undesired side effect of blooming or hazing. This phenomena is thought to result from the reaction between the highly reactive primary amine groups with atmospheric carbon dioxide and moisture to produce carbamates, resulting in scission of the curing agent polymer chain. Another problem that can occur with conventional primary amine curing agents in storage is that they may oligomerize, especially in hot environments. Thus, many amine curing agents have a problem with storage stability. To some extent, this problem can be ameliorated by reacting out many of the primary amine hydrogens. The drawback to this approach in the past has been that the reactivity of the curing agent was impaired because secondary amines are less reactive that the primary amines, such that accelerators had to be used to obtain adequate cure times, especially at low curing temperatures. Furthermore, many of the amine curing agent adducts formed to eliminate the presence of primary amine groups are poorly compatible with the epoxy resin such that induction times of 10 minutes to two hours were needed to compatibilize the epoxy resin composition with the curing agent composition.
It would be desirable to have a curing agent composition which is storage stable yet reactive enough to cure epoxy resins without external catalysts/accelerators in a wide range of curing temperatures and which can be applied to a substrate immediately upon mixing with the epoxy resin rather than waiting for an induction time to compatibilize the two components.